At the present time, in the third generation mobile communication system or the next generation mobile communication system, a wireless communication system has been discussed in the 3GPP (3rd Generation Partnership Project), and various provisions have been established.
In the 3GPP, a plurality of frequency bands are prescribed as frequency bands to be used. The prescribed frequency bands are exclusively assigned respectively to a plurality of business operators. The business operators use the assigned frequency bands to provide wireless communication services.
Of the business operators, some business operator is assigned with a wide bandwidth included in one prescribed frequency band. This business operator performs wireless communication using signals of the same frequency band. A signal process can be performed simply using one local oscillator signal, thus one oscillator is enough.
Of the business operators, some business operator secures only a narrow bandwidth, because the bandwidth is used mainly by other business operators. Because it is difficult for this business operator to sufficiently secure a frequency bandwidth in one frequency band, the business operator secures the narrow bandwidth in a plurality of frequency bands, thereby possibly securing an adequate frequency bandwidth. Accordingly, when wireless communication is performed using the plurality of frequency bands, different local oscillator signals are used for the plurality of bands, thus requiring a plurality of oscillators. Also when simultaneously receiving signals at different frequency bands, a plurality of oscillators are used. From this point, generally, a set of one oscillator and one frequency converter is used. Thus, when simultaneously receiving signals at different frequency bands, two reception paths are used.
Conventionally, when two signals at different frequency bands are synthesized to generate one single, a wireless communication device illustrated in FIG. 7 has been used. In this wireless communication device, as illustrated in FIG. 7, signals received through the two different reception paths are processed respectively by a signal processor 901 and a signal processor 902. Then, the processed signals are synthesized by a signal-synthesizing unit 903 to generate one signal.
As a technique for processing different signals, according to one technique, signals at different frequency bands are added to the main signal and sent together. Then, the receiver demodulates each of the added signals. Further, the frequency stability of the main signal is kept using a difference of the added signals. As a technique using a quadrature demodulator, as illustrated in FIG. 7, according to a conventionally-proposed technique using a direct conversion system, signal regeneration is performed, using a local signal whose phase is shifted by π/2 in frequency conversion for each of the received signals on an I (In-phase) axis and a Q (Quadrature) axis.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2000-151553
Patent Literature 2: Japanese Laid-open Patent Publication No. 2006-203686